(1) Field of the Invention
The present invention relates to a hitless path switching ring network, a hitless path switching transmission system, a node device for a hitless path switching ring network, and a failure occurrence-time hitless path switching transmission method in a ring network, which are capable of transmitting a signal without instantaneous hitting of the signal in a ring network where a plurality of node devices are interconnected in ring form through a work transmission line and a protection transmission line, even when switching of the transmission line is performed at the time of failure occurrence.
(2) Description of the Related Art
The ring network is constructed by a plurality of node devices interconnected through high-speed transmission lines (work and protection transmission lines).
Each node device in this ring network receives a signal sent from another network that is in a lower hierarchy, through a low-speed transmission line an d outputs the received signal onto the high-speed transmission line (work transmission line) toward another node.
Note that as an example, consider the case where a synchronous digital hierarchy (SDH) frame is transmitted along the high-speed transmission line within the ring network and each signal in each node device sent from a lower hierarchy is added to the payload of this SDH frame (high-group frame).
As a typical example of this ring network, a uni-directional protection switched ring (UPSR) has been proposed. If there is a failure in a transmission line along which a signal sent out from a certain node device is transmitted, the transmission line can be switched with no means so that the signal is transmitted to another node device, as if there were no failure.
FIG. 35 is a diagram showing a ring network 1-x1 of this UPSR type. The ring network 1-x1 shown in this diagram is constituted by node devices 10A-xxcx9c10D-x. In the node device 10A-x on the side of transmitting a signal (path 1), the signal is sent out onto a work transmission line (arrow x1 in FIG. 35) and is also previously sent out onto a protection transmission n line (arrow a x2 in FIG. 35) In the node device 10C-x on the receiving side, the signals received through the work and protection transmission lines are held in a work memory 20-x and a protection memory 30-x, respectively.
At the time of normal operation, for the signals read out from the work and protection memories 20-x and 30-x, the signal with better quality is selected and output by a path selecting section 40-x. Also, when a failure occurs in the work transmission line, the signal from the protection transmission line (i.e., the signal output from the protection memory 30-x) is automatically selected.
Thus, in the UPSR, the same signal is sent out onto the work transmission line and the protection transmission line, so when a failure occurs in the work transmission line, the output signal can be switched without instantaneous hitting by the path selecting section 40-x. However, the line (transmission line) capacity within the network is employed more than 1.5 times the case where a signal is sent out on either the work-transmission line or the protection transmission line (three or more nodes are employed).
On the other hand, compared with the aforementioned UPSR, another technique (bi-directional line switched ring (BLSR)) of effectively utilizing transmission lines has been proposed.
FIG. 36 is a schematic diagram showing a ring network of this BLSR type. In this ring network (hereinafter also referred to as simply a xe2x80x9cringxe2x80x9d) 1-x2 shown in the diagram, 4 node devices 10A-x2xcx9c10D-x2 respectively connected to other networks are connected and constructed in ring form through transmission lines.
In this ring network 1-x2, one-half its transmission line capacity within in the ring 1-x2 is employed in the work transmission line and the remaining half is employed in the protection transmission line. The ring network 1-x2 performs communication in the form of sending out a SDH frame in the east and west directions by the node devices (node devices on the transmitting side) 10A-x2xcx9c10D-x2. Also, if the node devices 10A-x2xcx9c10D-x2 detect a signal, which is output to another network, from the signals (added to the SDH frame) received through the trunk transmission line (between node devices), the node devices 10A-x2xcx9c10D-x2 will drop the detected signal to the other network. On the other hand, if a signal is received from another network, the node devices 10A-x2xcx9c10D-x2 will add the received signal to the SDH frame and send out the SDH frame onto the transmission line between the node devices.
Incidentally, if a section failure occurs in the work transmission line between the node devices 10B-x2 and 10C-x2, the ring network 1-x2 will loop back the signal, which is sent onto the work transmission line, at the node device, 10B-2 and send out the signal onto the protection transmission line on the side of the node device 10A-x2, after failure occurrence, as shown in FIG. 37. The signal, looped back and sent out onto the protection transmission line, is sent through the node devices 10A-x2 and 10D-x2 to the node device 10C-x2.
Note that the process of looping back a signal onto the protection transmission line at the time of section failure occurrence is controlled by the bytes K1 and K2 added to the section overhead (SOH) of a SDH frame.
Also, when the node device 10C-x2 detects a failure in the work transmission line, it instructs a loop back instruction to the node device 10B-x2 through a long path (i.e., via the node devices 10D-x2 and 10A-x2) with the bytes K1 and K2.
As mentioned above, in the ring network 1-x2, the node device 10B-x2 outputs a signal toward the node device 10A-x2, after receiving the bytes K1 and K2.
For instance, in the node device 10B-x2, a signal (path 3) coming in along a low-speed transmission line is sent out toward the node device 10C-x2 with the work transmission line at the time of normal operation. However, when a section failure occurs, the signal (path 3) coming in along the low-speed transmission line after failure occurrence is sent out toward the node device 10A-x2 with the protection transmission line. And in the node device 10C-x2, the signal (path 1) is output onto a low-speed transmission line.
Thus, in the BLSR, after failure occurrence, a section signal is sent out onto the protection transmission line in the opposite direction from the direction in which a signal is transmitted before failure occurrence, so that there is a possibility that the signal received at the node device 10C-x2 on the receiving side will be partially chopped. As a result, it becomes difficult to switch a transmission line without causing instantaneous hitting of a signal.
The present invention has been made in view of the aforementioned problems. Accordingly, it is the object of the present invention to enable switching from work transmission line to the protection transmission line without causing the occurrence of instantaneous hitting of a signal, when a failure occurs in the work transmission line in a ring network such as the aforementioned BLSR.
To achieve the aforementioned object of the present invention, there is provided a hitless path switching ring network comprising at least two node devices connected in ring form through a work-transmission line and a protection transmission line, wherein at the time of normal operation a signal, is transmitted with the work transmission line and at the time of failure occurrence in the work transmission line the signal can be transmitted with the protection transmission line in the opposite direction from the direction in which the signal was transmitted before failure occurrence. In order to cause the signal to be received from one of the node devices to the other of the node devices without instantaneous hitting of the signal at the time of failure occurrence, the one node device includes a first memory section for storing the signal being transmitted onto the work transmission line at the time of normal operation, and a first read control section for reading out the transmitted signal held before failure occurrence from the first memory section and sending out the transmitted signal through the protection transmission line in the opposite direction from the transmission direction employed before failure occurrence, at the time of failure occurrence in the work transmission line. Also, the other node device includes a second memory section for storing the signal received through the work transmission line at the time of normal operation, a third memory section for storing the signal received through the protection transmission line from the first read control section of the one node device at the time of failure occurrence, and a first phase adjusting section for matching a time phase of the received signal stored in the second memory section after failure occurrence with a time phase of the received signal stored in the third memory section before failure occurrence and outputting the received signal to the outside.
According to the hitless path switching ring network of the present invention, the first read control section of the one node device reads out the transmitted signal held before failure occurrence from the first memory section and sends out the transmitted signal through the protection transmission line in the opposite direction from the transmission direction employed before failure occurrence, at the time of failure occurrence in the work transmission line. Also, the first phase adjusting section of the other node device matches a time phase of the received signal stored in the second memory section after failure occurrence with a time phase of the received signal stored in the third memory section before failure occurrence and outputs the received signal to the outside. Therefore, switching of the transmission line can be performed without reducing transmission quality. In addition, the number of node devices can be increased and line utilities can be replaced.
To achieve the aforementioned object of the present invention, there is also provided a hitless path switching ring network comprising at least two node devices connected in ring form through a work transmission line and a protection transmission line, wherein at the time of normal operation a signal is transmitted with the work transmission line and at the time of failure occurrence in the work transmission line the signal can be transmitted with the protection transmission line in the same direction as the direction in which the signal was transmitted before failure occurrence. In order to cause the signal to be received from one of the two node devices to the other of the two node devices without instantaneous hitting of the signal at the time of failure occurrence, the one node device includes a fourth memory section for storing the signal being transmitted onto the work transmission line at the time of normal operation, and a second read control section for reading out the transmit ted signal held before failure occurrence from the fourth memory section and sending out the transmitted signal through the protection transmission line in the same direction opposite as the transmission di reaction employed be fore failure occurrence, at the time of failure occurrence in the work transmission line. Also, the other node device includes a fifth memory section for storing the signal received through the work transmission line at the time of normal operation, a sixth memory section for storing the signal received through the protection trans-mission line from the second read control section of the one node device at the time of failure occurrence, and a second phase adjusting section for matching a time phase of the received signal stored in the fifth memory section after failure occurrence with a time phase of the received signal stored in the sixth memory section before failure occurrence and outputting the received signal to the outside.
According to the hitless path switching ring network of the present invention, the second read control section of the one node device reads out the transmitted signal held before failure occurrence from the fourth memory section and sends out the transmitted signal through the protection transmission line in the same direction opposite as the transmission direction employed before failure occurrence, at the time of failure occurrence in the work transmission line. Also, the second phase adjusting section of the other node device matches the time phase of the received signal stored in the fifth memory section after failure occurrence with the time phase of the received signal stored in the sixth memory section before failure occurrence and outputs the received signal to the outside. Therefore, switching of the transmission line can be performed without reducing transmission quality. In addition, the number of node devices can be increased and line utilities can be replaced.
To achieve the aforementioned object of the present invention, there is also provided a hitless path switching transmission system comprising at least two node devices connected in opposition to each other through a work transmission line and a protection transmission line, wherein at the time of normal operation a signal is transmitted with the work transmission line and at the time of a failure occurrence in the work transmission line the signal is transmitted with the protection transmission line. In order to cause the signal to be received from one of the node devices to the other of the node devices without instantaneous hitting of the signal, the one node device includes a thirteenth memory section for storing the signal being transmitted onto the work transmission line at the time of normal operation, and a fifth read control section for reading out the transmitted signal held before failure occurrence from the thirteenth memory section and sending out the transmitted signal through the protection transmission line at the time of failure occurrence in the work transmission line, and the other node device includes a fourteenth memory section for storing the signal received through the work transmission line at the time of normal operation, a fifteenth memory section for storing the signal received through the protection transmission line from the fifth read control section of the one node device at the time of failure occurrence, and a fifth phase adjusting section for matching a time phase of the received signal stored in the fourteenth memory section after failure occurrence with a time phase of the received signal stored in the fifteenth memory section before failure occurrence and outputting the received signal to the outside.
According to the hitless path switching transmission system of the present invention, the fifth read control section of the one node device reads out the transmitted signal held before failure occurrence from the thirteenth memory section and sends out the transmitted signal through the protection transmission line at the time of failure occurrence in the work transmission line. Also, the fifth phase adjusting section of the other node device matches the time phase of the received signal stored in the fourteenth memory section after failure occurrence with the time phase of the received signal stored in the fifteenth memory-section before failure occurrence and outputs the received signal to the outside. Therefore, switching of the transmission line can be performed without reducing transmission quality. In addition, the number of node devices can be increased and line utilities can be replaced.
To solve the aforementioned problems, there is also provided a hitless path switching ring network node device connected in ring form with another node device through a work transmission line and a protection transmission line wherein at the time of normal operation a signal is transmitted with the work transmission line and at the time of a failure occurrence in the work transmission line the signal can be transmitted with the protection transmission line in the opposite direction from the direction in which the signal was transmitted before failure occurrence. In order to cause the signal to be received at the other node device without instantaneous hitting of the signal at the time of failure occurrence, the node device comprises: a first memory section for storing the transmitted signal at the time of normal operation; and a first read control section for, reading out, the transmitted signal held before failure occurrence from the first memory section and sending out the transmitted signal through the protection transmission line in the opposite direction from the transmission direction employed before failure occurrence, at the time of failure occurrence in the work transmission line.
According to the hitless path switching ring network node device of the present invention, the first memory section stores the transmitted signal at the time of normal operation, and the first read control section reads out the transmitted signal held before failure occurrence from the first memory section and sending out the transmitted signal through the protection transmission line in the opposite direction from the transmission direction employed before failure occurrence, at the time of failure occurrence in the work transmission line. Therefore, by making a phase adjustment at the other node device, switching of the transmission line can be performed without instantaneous hitting.
To solve the aforementioned problems, there is also provided a hitless path switching ring network node device connected in ring form with other node devices through a work transmission line and a protection transmission line wherein at the time of normal operation a signal is transmitted with the work transmission line and at the time of failure occurrence in the work transmission line the signal can be transmitted with the protection transmission line in the same direction as the direction in which the, signal was transmitted before failure occurrence. In order to cause the signal to be received at the other node devices without instantaneous hitting of the signal at the time of failure occurrence, the node device comprises: a fourth memory section for storing the signal being transmitted onto the work transmission line at the time of normal operation; and a second read control section for reading out the transmitted signal held before failure occurrence from the fourth memory section and sending out the transmitted signal through the protection transmission line in the same direction as the transmission direction employed before failure occurrence, at the time of failure occurrence in the work transmission line.
According to the hitless path switching ring network node device of the present invention, the fourth memory section for storing the signal being transmitted onto the work transmission line at the time of normal operation, and the second read control section for reading out the transmitted signal held before failure occurrence from the fourth memory section and sending out the transmitted signal through the protection transmission line in the same direction as the transmission direction employed before failure occurrence, at the time of failure occurrence in the work transmission line. Therefore, by making a phase adjustment at the other node device on the receiving side, switching of the transmission line can be performed without instantaneous hitting.
To solve the aforementioned problems, there is also provided a hitless path switching ring network node device. connected in ring form with another node device through a work transmission line and a protection transmission line wherein at the time of normal operation a signal is transmitted with the work transmission line and at the time of failure occurrence in the work transmission line the signal can be transmitted with the protection transmission line in the opposite direction from the direction in which the signal was transmitted before failure occurrence. In order to receive the signal from the other node device without instantaneous hitting of the signal at the time of failure occurrence, the node device comprises: a second memory section for storing the signal received through the work transmission line at the time of normal operation; a third memory section for storing the signal received through the protection transmission line from the other node device at the time of failure occurrence; and a first phase adjusting section for matching a time phase of the received signal stored in the second memory section after failure occurrence with a time phase of the received signal stored in the third memory section before failure occurrence and outputting the received signal to the outside.
According to the hitless path switching ring network node device of the present invention, the second memory section stores the signal received through the work transmission line at the time of normal operation, and the first phase adjusting section matches the time phase of the received signal stored in the second memory section after failure occurrence with the time phase of the received signal stored in the third memory section before failure occurrence and outputs the received signal to the outside. Therefore, by adjusting the phase of the transmitted signal sent out onto the protection transmission line at the other node, the signal can be output to the outside without instantaneous hitting.
To solve the aforementioned problems, in a hitless path switching ring network comprising at least two node devices connected in ring form through a work transmission line and a protection transmission line wherein at the time of normal operation a signal is transmitted with the work transmission line and at the time of failure occurrence in the work transmission line the signal can be transmitted with the protection transmission line in the opposite direction from the direction in which the signal was transmitted before failure occurrence, in order to cause the signal to be received at the other of the two node devices without instantaneous hitting of the signal at the time of failure occurrence, there is provided a failure occurrence time hitless path switching transmission method in the ring network wherein at the time of failure occurrence in the work transmission line, one node device of the node devices, which is transmitting the signal in a direction in which the failure occurred, retransmits the signal held before failure occurrence through the protection transmission line in the opposite direction; and the other node device matches a time phase of the signal received through the work transmission line after failure occurrence with a time phase of the received signal before failure occurrence retransmitted through the protection transmission line from the one node device and outputs the received signal to the outside.
According to the failure occurrence-time hitless path switching transmission method in the ring network of the present invention, at the time of failure occurrence in the work transmission line the one node device of the two node devices, which is transmitting the signal in a direction in which the failure occurred, retransmits the signal held before failure occurrence through the protection transmission line in the opposite direction. Also, the other node device matches a time phase of the signal received through the work transmission line after failure occurrence with a time phase of the received signal before failure occurrence retransmitted through the protection transmission line from the one node device and outputs the received signal to the outside. Therefore, switching of the transmission line can be performed without reducing transmission quality. In addition, the number of node devices can be increased and line utilities can be replaced.